The present invention relates generally to intraocular lens devices adapted for implantation in a human eye.
Intraoccular lens devices (hereinafter also referred to as IOLs) are well known and in many forms have been successfully implanted in human eyes following cataract surgery after the natural crystalline lens of the eye has been removed, as has been described for example in J. Jaffe, "Current Status of Intraocular Lenses," 51 Eye, Ear, Nose and Throat Monthly 290-96 (1972). However, excess weight and size of the IOLs caused failure of some of the early implants, and the ultimate success of this technique was due in part to the reduction in weight of the lens device.
Even though the weight of IOLs has been reduced in more recent devices developed in the art, the applicant is of the belief that a significant added advantage could be gained if their weight relative to the fluid inside the eye could be reduced to zero, that is, if the lens could be provided with neutral buoyancy with respect to the aqueous humor of the eye. Such a neutral buoyancy condition of the intraocular lens (that is, a condition in which the mean density of the IOL is equal to the density of the aqueous humor) would, it is felt, reduce the tremor, or shake, due to the fast saccadic movement of the eye, which in turn would likely reduce iris irritation and hence, possibly, a type of recurrent traumatic iritis. Neutral buoyancy also would tend to reduce the likelihood of the lens becoming a semi-missile inside the eye in the event of severe ocular trauma such as occurs in a car accident or other unexpected event causing a sudden impact to the head.
The natural crystalline lens itself has weight within the eye, that is, it does not achieve neutral buoyancy, but due to the hundreds of zonule fibrils coming from the ciliary body that support its entire periphery, the natural crystalline lens moves very little with large or sudden movements of the eye. However, some IOLs do not share this broad support, but instead are supported only by a few points of contact with the iris which carry the entire weight of the IOL. For example, the IOL may be supported by the pupilary sphincter, or by a suture, arm or loop attaching the IOL to the iris. Although the weight of the IOL may be very small, the few support points of iris contact experience high-pressure loading which can contribute to pressure necrosis and atrophy of the fragile iris.
Although some IOLs are supported entirely by the lens capsule zonular fibrils and therefore do not produce the aforementioned problems associated with the iris, this fixation technique is uncommonly used since the danger of dislocation of an implant supported solely by the lens capsule is high. Therefore irido-capsular fixation is more commonly utilized, whereby the lens is partially supported by the iris as well as the posterior capsular of a natural lens. In the latter case it would be desirable to utilize a lens of neutral buoyancy to lower the pressure imposed on the fragile iris.